In the field of mass analysis using an ion trap mass spectrometer or other apparatuses, a technique called the MS/MS analysis (or tandem analysis) has been recognized. In a general MS/MS analysis, an ion (target ion) having a specific mass-to-charge ratio (m/z) is first selected as a precursor ion from an object to be analyzed, and the precursor ion thus selected is dissociated by a collision-induced dissociation (CID) process. After that, a variety of product ions generated by the dissociation are mass analyzed to obtain the information on the mass and chemical structure of the target ion.
In recent years, samples having larger molecular weight than before have been analyzed with such an apparatus, and their chemical structures (compositions) have also tended to become more complicated. Hence, depending on the quality of the sample, ions are often not dissociated to have a sufficiently small mass by only a one-stage dissociation operation. In such cases, an MSn analysis may often be performed in which a dissociation operation is repeated multiple times (n−1 times) and the product ions finally generated are mass analyzed (refer to Patent Documents 1 and 2 for example). The mass analysis of a product ion by a single dissociation operation is an MS2 analysis, and a normal mass analysis without a dissociation can be described as an MS1 analysis.
In such an MSn analysis, the candidates for the molecular structure and composition of a target substance to be analyzed are narrowed down using basically both the composition formulae formed by the combination of elements deduced from the precursor ion's mass and the combinations of the elements deduced from the product ion's mass. However, even an apparatus capable of computing the mass with a certain level of high accuracy has the problem that, as the molecular weight of the target substance becomes larger, the refinement becomes more difficult and tends to leave more candidates, making it very difficult to ultimately determine the composition and structure of the target substance. In addition, if the number of candidates for a precursor ion and product ion is large during the process, it takes a very long time to perform an analysis to deduce the composition of the target substance.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. H10-142196
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2001-249114